Re: RF choke ferrite materials

Hi Marco,
                A very interesting question:

> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> 
> Hello all.
> Recently Mike Hammer posted on the Tesla-2 list an interesting address:
> http://www.bytemark-dot-com/amidon/
> It seems like they have in stock large ferrite toroids, at a feasible price ($
> 10 - 15) and no minimum order. This is a rare case, in my experience.
> Now my questions, about building a couple of protection chokes to be connected
> between the tank and the primary circuit.
> What kind of ferrite material should be selected? An iron-powder (mu about 10)
> to avoid saturation at high currents or a wide-frequency ferrite with a higher
> mu?

The iron powder cores have a distributed airgap in them. This 
enables them to handle a high level of DC. However, the greater the 
AC  component, the greater their losses. They heat very quickly with 
high ripple currents in SMPS applications. So if it's low Q chokes 
you want, they are a good bet but expect a lot of heating. I think I 
would try them with tough insulated wire dunked in oil or something 
like that.